The 20 trials assessed by Australian researchers lasted between two to eight weeks and involved 856 people consuming between 30-1080 mg of flavanols in 3-100 g of chocolate each day.

The researchers found that high flavanol chocolate or cocoa powder reduced blood pressure on average by 2-3mm Hg.

Compounds found in cocoa called flavanols are thought to increase amounts of nitric acid in the body, which causes blood vessel walls to relax and open, consequently cutting blood pressure.

Cocoa had been thought to provide blood pressure benefits after it was discovered that the natives of San Blas Island in Central American, who drink flavanol-rich cocoa drinks every day, had normal blood pressure regardless of age.

May complement other heart disease treatments

Lead researcher Karin Ried of the National Institute of Integrative Medicine in Melbourne, Australia, said: “Although we don't yet have evidence for any sustained decrease in blood pressure, the small reduction we saw over the short term might complement other treatment options and might contribute to reducing the risk of cardiovascular disease."

She said that longer term trials were needed to assess the effects on stroke and heart disease risk and determine any poetical side-effects of long term consumption.

"These trials should use flavanol-free products in the control groups to eliminate any potential effects of low-dose flavanol on blood pressure," she continued.

Adverse effects

Around 5% of people in the 20 trials reported adverse effects of cocoa/chocolate consumption, such as gastrointestinal complaints and distaste of the trial product. Only 1% of patients in the control groups reported complaints in comparison.

The researchers said it was difficult to determine he amount of chocolate needed to achieve blood pressure benefits as flavanol levels in chocolate can vary due to changes in the chocolate making process.

ConfectioneryNews.com previously reported on a study that identified stages in chocolate processing that could affect the quality of the final product, including type of cocoa tree, country of origin and pod storage. (See HERE
)

Milk and white chocolate

Dark chocolate has a higher concentration of cocoa flavanols compared to milk or white chocolate, by around 60%, according to an earlier study. (See HERE
)

Researchers of the current review said that lower flavanol chocolate, such as milk or white varieties, may have some minor beneficial effect on blood pressure, but a subset of trials evaluated had shorter trial periods and participants knew their allocated group.